The present invention relates generally to counterbalance systems for upwardly acting sectional doors. More particularly, the present invention relates to cable storage drums which pay out and retrieve cable interconnecting the door with the remainder of the counterbalance system during the closing and opening of a sectional door. More specifically, the present invention relates to cable storage drums having a small diameter and reduced length to minimize possible interference between the cable and door or door frame without sacrificing operational capabilities of the counterbalance system.
Spring counterbalance systems have been commonly used to counterbalance overhead doors such as sectional garage doors. For many years, sectional doors have employed torsional counterbalance systems using the rotational forces of this system to assist in controlling the lifting and lowering of the door by means of cables or other flexible members attached to the bottom of the door and to cable storage drums normally mounted proximate the ends of a drive tube or shaft of the counterbalance system. These cable storage drums manage and store the cable by providing guiding grooves that are machined or cast into the drums to guide the lift cables on and off of the cable storage drum and prevent the coils from rubbing against themselves or coiling on top of each other.
With these conventional systems, a single layer of cable is wrapped around the outside diameter of the cable storage drum. This single wrapping of the stored cable necessitates a drum length adequate to store the cable when the door is in the open position i.e. when the majority of the cable has been wound onto the drum. As can be appreciated, the diameter of the cable storage drum also affects the drum length needed to accommodate the stored cable but, the diameter of the cable storage drum is largely a matter of available space and other design factors. In some cases, a desired small diameter of the drum requires a drum of such a length that it causes the cable to pass in front of the door as it is wound. In these designs it is possible under certain circumstances for the cable to catch or hang up on the door.
A separate concern is raised by the winding and unwinding of the cable drum. Grooves in the drum""s surface have been used to space and guide the cables on and off of the drum to prevent the cables from abrading each other or from becoming entangled. Alternative designs have incorporated cable guides such as levelers, windlesses, and traversing devices. These devices typically guide the cable by imparting a lateral force to the cable by means of spring loaded members, hydraulic actuators, or by using the tension on the cable itself. While these guide devices adequately manage the cable on cable storage systems for some types of applications, they are somewhat complicated and expensive and typically require added space. Consequently, it is desirable to provide a cable storage drum that guides the cable as it is wound and unwound without the necessity of a separate complex guide mechanism.
Relatedly, it is known to use cable drums adapted to handle multiple layers of cable in hoists, winches and other applications where great lengths of cable must be handled. Cable drums used in counterbalance systems for sectional overhead doors employ relatively short cables so that single cable layer drums are universally employed to thereby avoid problems attendant the use of additional cable layers which increase the effective diameter of the drum thereby changing the torsional lever arm. The change in lever arm affects performance of the counterbalance system during opening and closing the door. When the cable is paid out, with the door in the closed position, in a conventional counterbalance system a large amount of force is necessary to lift the door. To compensate for this condition, installers often over tighten the springs to give the door an over-tensioned condition referred to as xe2x80x9chot off the floorxe2x80x9d causing the door to continue open after it is moved. The xe2x80x9chot off the floorxe2x80x9d condition is desirable for people who would otherwise have difficulty raising a door without an operator. But, the linear spring tension causes the door to be difficult to pull down from the open position. To endeavor to alleviate this problem, known designs add ropes or handles to the door to assist in moving the door from the open position.
Therefore, an object of the present invention is to provide a counterbalancing system for sectional doors which is highly compact and contemplates the storage of multiple layers of cable on the cable storage drums. Another object of the present invention is to provide such a counterbalancing system wherein the cable storage drums may be of such a reduced length due to the multiple layers of cable such that the cable storage portion of the cable drums need be no wider than the distance between the track system and the edge of the door, whereby the cable does not catch on or engage the door during opening and closing of the door. A further object of the invention is to provide such reduced length cable storage drums such that the cable is never visible from the outside of the door and never passes between the door and the door frame where it could hang up on or damage those structural elements.
Another object of the present invention is to provide a counterbalance system for sectional doors wherein a fixed structural flange with an undercut or reverse bevel on the cable storage drums effects proper wrapping of the cables. A further object of the present invention is to provide such a counterbalance system which provides control of the wrapping of the cables on the cable storage drums without springs, levers, gears, guides, traversing devices, or other additional moving parts associated with the drums or cables that might require adjustment or be subject to failure. Yet another object of the invention is to provide such a counterbalance system wherein the cable storage drums may remain of a compact design to accommodate limited space constraints while providing open access to the drums.
Still another object of the present invention is to provide a counterbalance system for sectional doors in which reduced force is required to move the door out of the open position due to the mechanical advantage achieved by stacking the cables in layers on the cable storage drums. A still further object of the invention is to provide such a counterbalance system which may be over-tensioned to provide continued movement of a door once opening movement commences while providing the reduced force requirement for moving the door from the open position. Yet another object of the invention is to provide such a counterbalance system wherein the cable storage drums can be of a reduced diameter without an increase in length or a cable drum of the same diameter and length can be used to store the cables of a much taller door. Another object of the invention is to provide a counterbalance system wherein the varied force imparted by layering the cables on the cable drums permits variations in the design of the counterbalance springs to achieve easier door opening and closing operations by the system.
Yet a further object of the invention is to provide a counterbalance system for sectional doors wherein the cable storage drum design allows layered storage of the cables without increased cable chaffing and noise during operation. Another further object of the invention is to provide a cable storage drum configuration which can be retrofitted on existing doors, can be easily and inexpensively manufactured, and is not prone to damage or wear which would impair operation or require replacement.
In general, the present invention contemplates a counterbalance system for an upwardly acting door movable on tracks between a closed position and an open position having, a drive tube adapted to be mounted above the door in the closed position, a cable drum assembly mounted proximate each end of the drive tube, a cable connecting each cable drum assembly and the door, a cylindrical member on the cable drum assembly, a cable receiving surface on the cylindrical member extending laterally between the door and the tracks and receiving multiple layers of the cable during movement of the door from the closed position to the open position, whereby the cable avoids engagement with the door during movement between the closed position and the open position.